It has long been known that malignant tumors are often characterized by substantially different mechanical properties than surrounding normal tissue. This accounts for the efficacy of palpation as a clinical technique to detect cancer in accessible regions of the body. Indeed, most tumors of the thyroid, breast, and prostate are still first detected by this centuries-old diagnostic technique. Unfortunately, small or inaccessible lesions cannot be detected by touch, and conventional diagnostic imaging methods such as ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) do not provide information that is in any way analogous. The goal of this proposal is to develop and validate a diagnostic imaging technique for quantitatively delineating mechanical properties of tissues. The proposed technique applies mechanical waves to tissue and measures regional elasticity by analyzing the pattern of wave propagation. A critical component of this new technique is a recently-developed method for directly observing propagating acoustic waves in tissue, using an MRI sequence with synchronous motion-sensitizing gradients. The central hypothesis of this work is that the proposed technique can be successfully implemented as a clinical tool and that it will be useful for detecting and characterizing focal and diffuse disease processes that may be difficult to investigate by other methods. The research plan includes investigations in the following areas (I) improving the MR acoustic wave imaging sequence, (2) developing effective methods for applying acoustic waves to tissue, (3) refining the required image processing methods, (4) studying the potential of the technique for tissue characterization, and (5) implementing the technique in human studies. The methods will encompass theoretical work, basic MRI pulse sequence development, device engineering, studies of animal and human tissue specimens, and trials with normal and patient volunteer's, special emphasis on optimizing the technique for breast cancer detection. If the research is successful, it will yield a new diagnostic imaging tool that may: (I) provide a means to noninvasively "palpate by imaging" regions of the body that are beyond the reach of the physician's hand, (2) delineate tumors before they are large enough to detect by touch, (3) provide greater sensitivity for assessing changes in tissue elasticity, and (4) provide a useful new quantitative tool for characterizing tissue.